Evaluating the biological interaction between MS and depression
Based on this and other studies, the joint effect of MS and depression on all-cause mortality may qualify as a biological interaction, Amber Salter, PhD, of the University of Texas Southwestern Medical Center, Dallas, wrote in an accompanying editorial.
“Biological interactions consider whether the joint effect of two factors follow an additive pattern, or the joint effect of two factors is greater than the sum of the individual effects for each factor alone,” she wrote. And though the interaction was not found to be present for vascular disease and cardiovascular mortality, it was for all-cause mortality.
“When warranted, the evaluation of biological interactions in future studies should be considered to provide insight on target subpopulations for interventions or test for potential mechanistic forms of interaction,” she added.
Dr. Salter highlighted the study’s strengths, including a large sample size and six controls matched to each MS patient. She also stated that the researchers’ inability to control for risk factors like body mass index and physical activity means the 14% increase in mortality “may not be a large absolute increase in mortality when other covariates cannot be considered.” In addition, their lack of data on suicide – and its association with depression – offers up the possibility that increases in mortality could be tied to a “potentially modifiable risk” as opposed to a biologically increased one.
In acknowledging their study’s limitations, the authors stated that body mass index, though an important vascular risk factor, has a “modest” association with mortality, and that the average annual suicide rate in the MS population – though higher than in the non-MS population – is still “relatively low.”
Two of the authors disclosed receiving support, including grants and research funding, from various institutions and organizations in the United Kingdom, the United States, and Canada, as well as several pharmaceutical companies. Dr. Salter reported no relevant disclosures.